Physics
Scientific paper
Mar 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982phdt........35m&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF TEXAS AT AUSTIN, 1982.Source: Dissertation Abstracts International, Volume: 43-03, Section: B,
Physics
91
Scientific paper
Spectrophotometric observations of 99 HII regions in 20 spiral and irregular galaxies are presented and discussed. The emission properties are shown to form a one-parameter sequence. The vast majority of the nebulae must be ionization-bounded. It is demonstrated that the most effective spectral sequencing index composed of line intensities from one atomic species is log ({O II} + {O III})/H(.)(beta). Theoretical dust-free models of HII regions are constructed to explain the variations of {O II}, {O III}, {N II}/{O II}, and {S II}/ {O II}. The oxygen abundance is found to be the underlying physical determinant of the spectrum of a nebula. If oxygen is primary, nitrogen must be a secondary product of nucleosynthesis superimposed on a seed of order 1 x 10('-6). Sulphur is identified as a primary product of nucleosynthesis. The visual continuum appears to be contributed mainly by non-ionizing supergiants in the embedded OB associations. The population of supergiants may increase with the metal abundance. The extinction does not correlate with the metal abundance, probably because it is dominantly due to surrounding clouds. A metal-poor Sbc galaxy (NGC 3344) and two metal-rich Scd galaxies (NGC 3184 and NGC 6946) abundances. The total colour of a galaxy reddens with increasing average metal abundance. Metal abundances are found to correlate with surface mass densities, but do not appear to be related to large-scale dynamical phenomena such as density waves or angular velocity shear. It is suggested that a metal abundance gradient arises simply from a gradient in the formation rate of massive stars, set by the radial distribution of the disk mass. The empirical abundance calibration of log ({O II} + {O III}) is revised to assess the correlation of oxygen abundances with gas fractions. The disks of galaxies at stage cd appear to have evolved as isolated systems. Disks in Sbc galaxies show considerable scatter in abundances at a limiting gas fraction of about 0.01, possibly as a result of infall of metal-enriched spheroidal material to the inner zones.
No associations
LandOfFree
The Chemistry of Galaxies. does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Chemistry of Galaxies., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Chemistry of Galaxies. will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1019967